Hmmm ... let's see how we can explain this: Chocolate is full of fat, sugar and calories -- and eating it regularly makes you thinner.

Score!

A new study in the March 26 issue of the Archives of Internal Medicine showed that people who ate chocolate more frequently, such as every day, weighed less on average than those who ate it less regularly.

The study of 1,000 adults who were, on average, middle-aged, exercised three times a week and ate chocolate twice a week, was intended to study cholesterol. However in tracking cholesterol, the study also asked subjects how often they ate chocolate, among other questions on how much they exercised, how much they ate overall and where their dietary fats came from.

Most surprisingly, the people who ate chocolate the most often had lower body mass indexes, even though they ate more calories overall and did not have different exercise habits from those who ate the least amount of chocolate.

On average, those who ate five servings of chocolate a week weighed about five to seven pounds less than those who ate none, said Beatrice A. Golomb, the study's lead author and an associate professor of medicine at the University of California, San Diego. The researchers did not break down their chocolate consumption into dark, milk or white varieties, though past studies have shown greater benefits from dark chocolate than milk or white.

The researchers were not sure of the exact cause, but even when they accounted for possible hidden causes such as age, gender, depression, vegetable consumption, and fat and calorie intake, the effect still held. “It didn’t matter which of those you added, the relationship remained very stably significant,” said Dr. Golomb, who surmises that antioxidants and other compounds in chocolate boost the metabolism, which outweighs the weight-increasing effect of the extra calories.

In recent years, studies have uncovered other health benefits to chocolate, including lower blood pressure and cardiovascular risk, improved cholesterol levels and insulin regulation.

Dr. Golomb got the idea for the study when she was at a conference seated next to a nutritionist. “This lovely chocolate dessert cart came out, and she looked at it forlornly and said, ‘Too bad it has all these calories,’ ” she told The New York Times.

Dr. Golomb had seen research on animals showing that polyphenols, a type of antioxidant that abounds in chocolate, especially dark chocolate, boosted muscular performance and lean muscle mass and could cause weight loss even if the animal did not change its calorie consumption or exercise frequency. That prompted Dr. Golomb to suspect that chocolate increased metabolism at least as much as the extra calories would increase weight, giving chocolate a neutral effect on body weight.

“We found something slightly more favorable than that,” she told the Times.

But the important takeaway is that the regularity of the consumption is the key, not the size of a single serving. So, eating a full bar of chocolate in one sitting likely won't provide a health benefit, but eating the same bar over the course of the week will.